Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F5/00—Dryer section of machines for making continuous webs of paper
  • D21F5/02—Drying on cylinders
  • D21F5/022—Heating the cylinders
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F5/00—Dryer section of machines for making continuous webs of paper
  • D21F5/02—Drying on cylinders
  • D21F5/022—Heating the cylinders
  • D21F5/024—Heating the cylinders using electrical means
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F5/00—Dryer section of machines for making continuous webs of paper
  • D21F5/02—Drying on cylinders
  • D21F5/022—Heating the cylinders
  • D21F5/028—Heating the cylinders using steam
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F5/00—Dryer section of machines for making continuous webs of paper
  • D21F5/02—Drying on cylinders
  • D21F5/06—Regulating temperature
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F26—DRYING
  • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
  • F26B13/00—Machines and apparatus for drying fabrics, fibres, yarns, or other materials in long lengths, with progressive movement
  • F26B13/008—Controlling the moisture profile across the width of the material
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F26—DRYING
  • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
  • F26B13/00—Machines and apparatus for drying fabrics, fibres, yarns, or other materials in long lengths, with progressive movement
  • F26B13/10—Arrangements for feeding, heating or supporting materials; Controlling movement, tension or position of materials
  • F26B13/14—Rollers, drums, cylinders; Arrangement of drives, supports, bearings, cleaning
  • F26B13/18—Rollers, drums, cylinders; Arrangement of drives, supports, bearings, cleaning heated or cooled, e.g. from inside, the material being dried on the outside surface by conduction
  • F26B13/183—Arrangements for heating, cooling, condensate removal

Definitions

• the invention relates to a method for drying a moving web of material at a paper or board machine, in which the web is dried with a heated drying cylinder transverse to the direction of travel of the web, past which the web is being led.
• the invention relates to an apparatus, with which the method can be applied.
• stock is continuously fed to an endless wire for forming a web of fibre material.
• the generated continuous web is transferred from the wire to the compression section of the paper or board machine, and further to the drying section of the machine, in which the web is typically dried by several heated drying cylinders successive in the direction of travel of the web.
• the drying can be followed by the gluing of the web, the drying of the glue, the calendering of the web for tightening or polishing its sur- face and, finally, the rolling of the finished web to a roll core as a so-called machine roll.
• the situation is most often such that the moisture of the web arriving at the drying section of the machine or travelling through its successive drying cylinders in the drying section is not uniform, but there are variations in the transverse direction of the web.
• the transverse moisture profile of the web is convex, which has been illustrated in Figure 4 of the patent drawings to be explained in more detail later.
• Another phenomenon shown as irregularities in the moisture profile of the web are the longitudinal moisture lines of the web, i.e. rather narrow longitudinal zones, in which the moisture of the web is clearly higher than in the areas immediately on both sides of the zone in question.
• the moisture lines typically originate from the wire section of the machines, in which the web was formed, resulting thus, for example, from local dis- turbances caused by blockages in the removal of water in the transverse direction of the wire.
• the moisture lines are shown as upwards extending peaks in the transverse moisture profile of the web according to Figure 5 of the claims.
• the object of the present invention is to solve the said problem caused by the ir- regular moisture profile of the web, especially by the longitudinal moisture lines of the web in a simpler and, for the use of energy, in a more inexpensive manner.
• the balancing of the moisture profile of the web i.e. the moisture differences in the transverse direction of the web is arranged to occur when drying the web in the drying section of the paper or board machine, the solution consist- ing essentially of independently adjusting the temperature of the drying cylinder at different locations in its longitudinal direction for balancing, in connection with the drying, the moisture differences in the transverse direction of the web which are due to moisture lines in the longitudinal direction of the web that are generated upon forming the web on the wire.
• the invention offers an option to tailor the heating effect applied to the web from the drying cylinder according to the moisture profile in question of the web, i.e. to apply a stronger heating to the locations of the web that are distinguished in the moisture profile is wetter than others and, respectively, a milder heating to those places that are drier than the others.
• the result is a straightening of the moisture profile of the web in connection with the drying process; in an ideal case, changing the profile to be linear so that there will be no moisture differences in the transverse direction of the web that is fully dried.
• the basic objective of the invention is to adjust the temperature of the drying cylinder so that it is possible with the adjustment to eliminate longitudinal moisture lines of the paper or board web that are generated in the wire section of the machine when forming the web.
• the technical solution suitable for this purpose is to place resistance wires at suitable relatively dense intervals to different locations in the longitudinal direction of the drying cylinder and to adjust the electric current travelling in each resistance wire independently, irrespective of the other wires.
• the heating of the cylinder and the drying effect caused by this can be intensified at the locations in the longitudinal direction of the cylinder, i.e. the transverse direction of the web, in which the moisture lines are located.
• the balancing of the moisture lines typically includes that the temperature of the cylinder is adjusted higher at two or more locations in the longitudinal direction of the drying cylinder than at locations immediately on both sides of the first- mentioned locations for balancing the moisture differences due to two or more moisture lines in the longitudinal direction of the web.
• the heating efficiency of the drying cylinder in the middle area of the cylinder can be generally arranged to be higher than at its opposite ends, in which case the cylinder will balance the moisture differences of the web that is wetter in the middle and drier at its edges.
• the general problem caused by air flows and appearing as convexity of the moisture profile of the web can thus be solved.
• a practical solution can be, for example, to divide the interior of the drying cylinder into successive zones in the lon- gitudinal direction of the cylinder so that heating vapour can be fed to different zones independently.
• the hottest vapour can be fed to the middlemost zone of the cylinder drying the middle section of the web, and the zones symmetrically on both sides of it can be supplied gradually with vapour with a lower temperature so that the heating vapour with the lowest temperature always effects at the oppo- site edges of the web.
• One advantageous embodiment option of the invention is to combine the said two ways of heating in the same drying cylinder.
• the vapour heated into different temperatures and led to the different zones in the cylinder can take care of the general balancing of the convex moisture profile of the web, at the same time as the longitudinal moisture lines distinguishing as peaks from the convex moisture profile can be separately eliminated by resistance wires placed in the casing of the cylinder.
• the apparatus of the invention for drying a moving web of material at a paper or board machine which apparatus comprises at least one heated drying cylinder transverse to the direction of travel of the web that is arranged to travel past the drying cylinder, is especially characterised in that resistance wires extensing annularly around the cylinder have been arranged at different locations in the longitudinal direction of the drying cylinder, the electric current being independently adjustable in each of the wires so that the temperature of the drying cylinder can be adjusted independently at different locations in its longitudi- nal direction for balancing in connection with the drying moisture differences occurring in the transverse direction of the web, the differences due to moisture lines in the longitudinal direction of the web.
• Figure 1 is a longitudinal section of a drying cylinder operated by heating vapour and applicable to the drying of a paper web;
• Figure 2 shows a partly cut view of a drying cylinder of the invention operated by electrical resistors and applicable to the drying of a paper web;
• Figure 3 presents the drying of a paper web with the drying cylinders in the drying section of a paper machine
• Figure 4 presents the moisture profile of the paper web to be dried in the transverse direction of the web, the web being wetter in the middle section than at its edges;
• Figure 5 is a moisture profile of a web similar to Figure 4, including also moisture lines in the longitudinal direction of the web;
• Figure 6 presents the ideal moisture profile of the web after the drying step.
• FIG. 1 is a principle drawing of a drying cylinder 1, which is part of the drying section of a paper machine, the purpose of the drying cylinder being the drying of the paper web that has been formed in the wire section of the machine and that has travelled through the compression section of the machine.
• the drying cylinder 1 comprises a longitudinal cylindrical casing 2, partitions 5 that divide the interior 3 of the cylinder into successive departments or zones 4, 4', 4" in its longitudinal direction, and end walls 6 closing the ends of the cylinder.
• the cylinder has been divided into three successive zones, namely the middle zone 4 and the edge zones 4', 4" located symmetrically on both sides of it but, in practice, the number of partitions 5 and the zones 4 separated by them may be considerably larger.
• the heating of the drying cylinder 1 for achieving a drying effect applied to the pa- per web travelling past the cylinder is performed by heating vapour led through the interior 3 of the cylinder.
• vapour flow 8 with the lower temperature has again been led from the end of the cylinder to its first edge zone 4' to heat the cylinder casing 2 in the section of this zone and further, through channels 11 penetrating the middle zone 4 of the cylinder to the second edge zone 4" to respectively heat the cylinder casing also in this section of the zone, and finally out from the opposite end of the cylinder.
• the heating of the casing 2 of the drying cylinder 1 is arranged to occur with independently adjustable resistance wires 12 that extend around the casing and are distributed over the length of the casing at equal intervals.
• the distance of the wires can be 1 - 30 cm, preferable 2 - 20 cm, and most preferably 3 - 15 cm.
• the elec- trie current travelling in the resistance wire or wires by the moisture line will be increased in relation to the adjacent wires at the same time as the general need of drying the web can be attended to by other adjusting of the wires, for example so that a stronger heating is generally applied to the middle section of the web than to the edges.
• vapour flows penetrating the cylinder can be used for heating the middle section of the casing hotter than the edge zones at the same time as the precise adjustment of the heating for making the casing at certain locations hotter than in the surroundings, especially for eliminating the longitudinal moisture lines of the web, can be achieved by the resistance wires in the casing.
• FIG 3 is a principle drawing of the drying of a wet paper web 13 with the drying cylinder 1 in the drying section of a paper machine.
• the structure and operation mode of the drying cylinders 1 are principally similar to those in Figure 1 , but the cylinders have been divided into seven successive zones 4 by the partitions 5 illustrated by broken line, the heating vapour flows being led through the cylinder via the said zones.
• the longitudinal zones 14 of the paper web 13 to be dried, corresponding to the successive zones 4 of the cylinder separated by the partitions 5 have been shown with broken lines 15 in Figure 3.
• the drying effect achieved by separate vapour flows is most strongly applied to the middlemost longitudinal zone of the web 13, abating towards the edges of the web.
• the convection of heat in the casing of the cylinder balances the drying effect so that the drying of the web does not occur progressively in accordance with the zones, but the drying effect weakens by gliding more or less from the centre of the web towards its edges.
• FIG 4 illustrates a typical transverse moisture profile 16 of the web to be dried, i.e. moisture in the direction of width of the web at the beginning of the drying. It can be seen that the web is wetter at its centre than at its opposite edges.
• longitudinal moisture lines which are distinguished as upwards directing peaks 17 in the profile.
• smoothing of the moisture profile 16 i.e. the general straightening of the profile and the elimination of the moisture lines appearing as peaks 17 can be achieved by drying the web according to the invention.
• the profile 16' will be horizontal according to Figure 6, i.e. the moisture content of the finished dried web is constant.

Landscapes

• Engineering & Computer Science (AREA)
• Textile Engineering (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Paper (AREA)
• Drying Of Solid Materials (AREA)

Priority Applications (5)

Applications Claiming Priority (2)

Publications (1)

Family

ID=34803229

Family Applications (1)

Country Status (7)

Cited By (1)

Families Citing this family (1)

Citations (8)

Family Cites Families (9)

• 2005
  • 2005-07-20 FI FI20050774A patent/FI124614B/sv not_active IP Right Cessation
• 2006
  • 2006-07-20 EP EP06778485.0A patent/EP1910615B1/en not_active Not-in-force
  • 2006-07-20 US US11/988,553 patent/US20090133282A1/en not_active Abandoned
  • 2006-07-20 PL PL06778485T patent/PL1910615T3/pl unknown
  • 2006-07-20 WO PCT/FI2006/000262 patent/WO2007010088A1/en active Application Filing
  • 2006-07-20 CA CA2614011A patent/CA2614011C/en not_active Expired - Fee Related
  • 2006-07-20 ES ES06778485T patent/ES2427353T3/es active Active

Patent Citations (8)

Non-Patent Citations (1)

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